Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.94   11.663%   $68.0474   $68.05   $68.05   $68.00  
  Purchase #2 $38.50   8.170%   $41.6455   $41.65   $41.65   $41.60  
  Purchase #3 $164.97   7.756%   $177.7651   $177.77   $177.75   $177.80  
  Purchase #4 $10.27   8.487%   $11.1416   $11.14   $11.15   $11.10  
  Purchase #5 $84.88   8.680%   $92.2476   $92.25   $92.25   $92.20  
  Purchase #6 $171.71   9.713%   $188.3882   $188.39   $188.40   $188.40  
  Purchase #7 $250.82   13.458%   $284.5754   $284.58   $284.60   $284.60  
  7 purchase totals = $782.09       $863.8108   $863.83   $863.85   $863.70